JP2003113138A - Method for distilling (meth)acrylic acid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of inhibiting polymerization of monomer(s) frequently occurring at the separation/refining of acrylic monomers, particularly to form an atmosphere inside a distillation column for the acrylic monomers hard to polymerize at the start or restart of distillation operation. SOLUTION: This method for distilling/refining the acrylic acid, methacrylic acid or ester(s) thereof by the use of the distillation column, involves wetting the inner wall surface of the distillation column with a polymerization inhibitor- containing liquid in advance followed by starting the operation of the distillation column.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for distilling acrylic acid, methacrylic acid or their esters (the substance to be distilled in the present invention may be abbreviated as “acrylic monomer” hereinafter). More specifically, the present invention relates to a method for preventing polymerization of a monomer that often occurs during separation and purification of an acrylic monomer obtained by catalytic vapor phase oxidation of propylene or isobutylene by distillation.

[0002]

2. Description of the Related Art A distillation method is generally used as a method for separating and purifying acrylic monomers. In recent years, high-performance packings have been developed for the purpose of improving the separation efficiency of distillation, increasing the throughput, etc., and have begun to be used in distillation columns in various processes.
However, the acrylic monomer is extremely easy to polymerize, and the formation of a polymer in the distillation column has been a serious problem both in the conventional tray type distillation column and particularly in the high performance packed column. Conventionally, as a method for preventing generation of acrylic monomer polymer, improvement of tray structure (JP 2000-300903A), use of special polymerization inhibitor (JP 7-53449A)
However, long-term continuous operation is still difficult,
Periodic inspections and repairs accompanied by outages were required. Polymers are often generated from the beginning of operation of the distillation column, and once the polymer is generated, the gas-liquid flow is obstructed, and the phenomenon that the generation of the polymer is accelerated is often seen.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for preventing the polymerization of monomers which often occurs during the separation and purification of acrylic monomers. In particular, when starting or resuming the distillation operation, it is to provide a means for forming an atmosphere in which the acrylic monomer is difficult to polymerize inside the distillation column.

[0004]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the inventors of the present invention have found that once a polymer is produced, the inside of the tower is partially blocked, which impedes the flow of gas and liquid. It was found that this is a cause of promoting the formation of a further polymer. Then, it is extremely important to prevent the polymerization at an early stage of the start of distillation of the acrylic monomer, and the inventors have found that the above object can be achieved by devising the usage mode of the polymerization inhibitor, and completed the present invention.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The gist of the present invention is a method for distilling acrylic acid, methacrylic acid or their esters in a distillation column, in which the inner wall surface of the distillation column is previously wetted with a liquid containing a polymerization inhibitor. Then, the method for distillation of acrylic acid, methacrylic acid or their esters is characterized in that the operation of the distillation column is started thereafter.

More specifically, in the present invention, the aqueous solution of acrylic acid or methacrylic acid obtained by vapor-phase catalytic oxidation of propylene or isobutylene and absorbing the oxidation reaction mixture with water is concentrated in the presence of an azeotropic agent. In the operation of purifying the obtained acrylic acid or methacrylic acid in a distillation column to produce high-purity acrylic acid or methacrylic acid, in the operation including stopping and starting the distillation column, the inner wall surface of the distillation column In a method of distilling and refining acrylic acid or methacrylic acid, which comprises previously wetting with a liquid containing a polymerization inhibitor, and then starting operation of the distillation column. Furthermore, the present invention is also characterized by the type of distillation column, the method of supplying the polymerization inhibitor, the selection of the liquid containing the polymerization inhibitor, and the like.

The mixture to be distilled in the present invention is acrylic acid, methacrylic acid or their esters, that is, acrylic monomers. For example, propylene or isobutylene is subjected to vapor-phase catalytic oxidation in the presence of a Mo-Bi-based composite oxide catalyst to produce acrolein or methacrolein, and further subjected to vapor-phase catalytic oxidation in the presence of a Mo-V-based composite oxide catalyst. Acrylic acid or methacrylic acid obtained as a result can be mentioned. At this time, even if the pre-stage reaction that oxidizes propylene to mainly produce acrolein and the post-stage reaction that oxidizes acrolein to produce mainly acrylic acid are carried out in separate reactors, a catalyst for carrying out the pre-stage reaction in one reactor The reaction may be performed by simultaneously filling the catalyst for the second-stage reaction and the catalyst for the second-stage reaction. Further, acrylic acid ester or methacrylic acid ester obtained in the step of producing the ester from acrylic acid or methacrylic acid is used. Examples of acrylic acid esters include methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, tertiary butyl acrylate, 2-ethylhexyl acrylate, 2-acrylic acid acrylate.
Examples thereof include hydroxyethyl, 2-hydroxypropyl acrylate, methoxyethyl acrylate, and the like, and similar compounds can be exemplified as the methacrylic acid esters.

These unpurified acrylic monomers include
Dimers and trimers of acrylic monomers, their esterified products, maleic anhydride, benzaldehyde, β-hydroxypropionic acid, β-hydroxypropionic acid esters, β-alkoxypropionic acid, β-alkoxypropionic acid ester, etc. The content of the acrylic monomer containing high boiling impurities and supplied to the distillation column is usually 2% by weight or more, preferably 5% by weight or more, and more preferably 10% by weight or more. Despite the low concentration of acrylic monomer,
The mixed composition formed with these impurities and / or water is extremely easy to polymerize under the temperature and pressure conditions in the column where the distillation treatment is carried out. Moreover, such polymerization is likely to occur at the beginning of the distillation operation. Therefore, the applicable range of the present invention is wide, and a very large effect is exhibited even in the treatment of a process liquid containing a small amount of an acrylic monomer. That is, the distillation of the acrylic monomer referred to in the present invention is typically a step of obtaining a high-purity acrylic monomer (purification step)
However, the present invention is not limited to this and is also applied to a step (separation step) of recovering a component rich in an acrylic monomer from a mixture containing an acrylic monomer.

Next, description will be made with reference to the drawings. FIG. 1 is an example of a process flow diagram for producing acrylic acid from propylene as a raw material. The symbols and numbers in the figure are as follows. A: Acrylic acid collection tower B: Dehydration tower C: Light-boiling separation tower (acetic acid separation tower) D: High-boiling separation tower (acrylic acid purification tower) E: High-boiling decomposition reactor 1 to 3: Polymerization inhibitor supply line 4: Oxidation reaction gas containing acrylic acid 5: Acrylic acid aqueous solution 11: Crude acrylic acid 15: Acrylic acid extraction line 19: High-purity acrylic acid extraction line

Acrylic acid-containing gas obtained by catalytic vapor-phase oxidation of propylene and / or acrolein with a molecular oxygen-containing gas is passed through line 4 to the acrylic acid collection tower A.
And contacted with water to obtain an aqueous acrylic acid solution. Next, the acrylic acid aqueous solution is supplied to the dehydration tower B. In the dehydration tower,
An azeotropic agent is supplied, an azeotropic mixture consisting of water and an azeotropic agent is distilled from the top of the column, and acrylic acid containing acetic acid is obtained from the bottom of the column. The azeotropic mixture composed of water and the azeotropic agent distilled from the top of the dehydration tower is introduced into the storage tank 10, where it is separated into an organic phase mainly composed of the azeotropic agent and an aqueous phase mainly composed of water. The organic phase circulates in the dehydration tower B. On the other hand, the aqueous phase can be effectively utilized by circulating it through the line 7 into the acrylic acid collection tower A and using it as the collected water to be brought into contact with the acrylic acid-containing gas. If necessary, replenish water from line 8. Further, in order to recover the azeotropic agent in the process liquid in line 7, it may be circulated to the acrylic acid collection tower A via an azeotropic agent recovery tower (not shown).

The crude acrylic acid extracted from the bottom of the dehydration tower B via the line 11 is introduced into a light boiling separation tower (acetic acid separation tower) C in order to remove residual acetic acid. Here, acetic acid is separated and removed from the tower top via lines 12 and 13. Since acetic acid in line 13 contains acrylic acid, some or all may be returned to the process. On the other hand, acrylic acid containing substantially no acetic acid is obtained from the bottom of the column through line 14. Since this acrylic acid has a considerably high degree of purity, it can be used as it is as a raw material for producing an acrylic acid ester, or in some cases, it may be made into a product via line 15. In order to obtain even higher purity acrylic acid, it is introduced into a high boiling separation column (acrylic acid purification column) D via line 16 to separate and remove high boiling point substances from line 17, and high purity acrylic acid is added to line 18. It can be obtained through 19. The high-boiling substance in the line 17 is introduced into the high-boiling decomposition reactor E, and a part of it is recovered as acrylic acid from the line 20 in the process.
The high boiling substance is separated and removed from the line 21. In the present process, the liquid containing the polymerization inhibitor is supplied from any one of lines 1 to 3 or a plurality of lines.

FIG. 2 is another example of a process flow diagram for producing acrylic acid. This is a process in which the dehydration column B and the light boiling separation column (acetic acid separation column) C in FIG. 1 are combined into one distillation column F, and the flow of substances is basically the same as in FIG.

FIG. 3 is another example of a process flow diagram for producing acrylic acid. A: Acrylic acid collection tower G: Dispersion tower D: High boiling separation tower (acrylic acid purification tower) H: High boiling removal tower K: Solvent purification tower 1-3: Polymerization inhibitor supply line 4: Contains acrylic acid Oxidation reaction gas 5, 11: Acrylic acid-containing solution 13: High-purity acrylic acid extraction line

Acrylic acid-containing gas obtained by catalytic gas-phase oxidation of propylene and / or acrolein with a molecular oxygen-containing gas is passed through line 4 to the acrylic acid collection tower A.
And then contacted with a solvent to obtain an acrylic acid-containing solution.
Next, the acrylic acid-containing solution is supplied to the stripping tower G. In the stripping tower G, a gas (a gas in the line 6 discharged from the top of the acrylic acid collection tower A, or a gas after oxidizing and removing organic substances in the gas in the line 6 etc.) is supplied from a line 10. Then, water and acetic acid are distilled from the tower top, and acrylic acid containing a solvent is obtained from the tower bottom. Water and acetic acid distilled from the top of the stripping tower G are introduced into the acrylic acid collection tower A, and water and acetic acid are finally discharged from the top of the acrylic acid collection tower A. From the bottom of the stripping tower G, through a line 11, to obtain high-purity acrylic acid, it is introduced into a high-boiling separation column (acrylic acid refining tower) D to separate and remove high-boiling substances from a line 14 to obtain high-purity acrylic acid. The acid can be obtained via line 13. The high-boiling substances in the line 14 are specifically maleic anhydride, benzaldehyde, etc., and are introduced into the high-boiling removal column H, and these high-boiling substances are discharged from the line 16. From the bottom of the column, the solvent is introduced into the solvent refining column K via line 17. The recovered solvent is returned from the top of the column to the acrylic acid collection column A through the line 7, and a part or most of it is directly fed from the line 17 to the line 7
It may be returned to the acrylic acid collection tower A via (not shown). Further high-boiling substances are separated and removed from the bottom of the column via line 18. The liquid containing the polymerization inhibitor is supplied from any one of lines 1 to 3 or a plurality of lines.

FIG. 4 is an example of a process flow diagram for producing an acrylic ester. The symbols and numbers in the figure are as follows. L: esterification reactor M: acrylic acid separation tower N: high boiling decomposition reactor Q: alcohol extraction tower P: alcohol recovery tower R: light boiling separation tower S: ester purification tower 1-3: polymerization inhibitor supply line 31 : Acrylic acid supply line 32: Alcohol supply line 33: Esterification reaction mixture 35: Circulating acrylic acid 37: High boiling point impurity extraction line 39: Crude acrylic acid ester extraction line 41: Water supply line 42: Recovered alcohol water Line 46: Acrylic ester product extraction line

Acrylic acid from line 31, alcohol from line 32, circulating acrylic acid from line 35, and circulating alcohol from line 48 are supplied to the esterification reactor L, respectively. The esterification reactor L is filled with a catalyst such as a strongly acidic ion exchange resin. The esterification reaction mixture consisting of the produced ester, unreacted acrylic acid, unreacted alcohol, and produced water is extracted via line 33 and supplied to the acrylic acid separation column M. The bottom liquid containing substantially all unreacted acrylic acid is withdrawn from the acrylic acid separation column M via a line 34 and is supplied to the esterification reactor L as a circulating liquid via a line 35. Part of the bottom liquid is line 3
It is supplied to the high boiling decomposition reactor N via 6 and the valuable material obtained by the decomposition is circulated to the process via a line 40. The location within the cycled process depends on the process conditions. High boiling impurities such as a polymer are removed from the system through the line 37. Further, from the top of the acrylic acid separation tower M,
The produced ester, unreacted alcohol, and produced water are distilled off via the line 38. A part of the effluent is circulated to the acrylic acid separation column M as a reflux liquid, and the rest is supplied to the extraction column Q via the line 39. Water for alcohol extraction is supplied from the line 41, and water containing alcohol recovered through the line 42 is supplied to the alcohol recovery tower P. The recovered alcohol is circulated to the esterification reactor via line 48.

From the line 43, the crude acrylic acid ester is supplied to the light boiling separation column R. The light-boiling substance containing acrylic acid ester is extracted from the line 44 and circulated into the process. The location within the cycled process depends on the process conditions. The crude acrylic acid ester from which the light-boiling substances have been removed passes through line 45 to the acrylic acid ester product purification tower S.
Is supplied to. High-purity acrylic ester is obtained from the top of the column via line 46. The liquid containing some high-boiling substances from the bottom of the column usually contains a large amount of acrylic acid, and thus is withdrawn through the line 47 and circulated into the process. The location within the cycled process depends on the process conditions. In this process, the liquid containing the polymerization inhibitor is added to lines 1-3.
It is supplied from any one or a plurality of lines.

FIG. 5 shows an example of a crude acrylic monomer distillation column and its associated equipment. The numbers in the figure are as follows. 51: Distillation column 52: Packing layer, or distillation column tray, or packing,
Combined use of distillation column tray 53: Inhibitor air supply line 54: Heat exchanger for cooling overhead gas 55: Heat exchanger for cooling vent gas 56: Reflux tank 57: Distributor 58: Reboiler (heat exchanger for heating) 59: Polymerization Inhibitor-containing liquid tank 60: Acrylic monomer (raw material) supply line 61 1, 61 2, 61 3: Polymerization inhibitor supply line 62: Top liquid extraction line 63: Bottom liquid extraction line 64: Vent gas Discharge line The liquid containing the polymerization inhibitor is supplied from any one of line 61 1, line 61 2 and line 61 3 or a plurality of lines. 53 is also installed at one or more places in various parts of the distillation depending on the conditions of the distillation column.

The distillation column to which the present invention is applied is all distillation apparatuses in which acrylic acid or acrylic acid ester participates in gas-liquid equilibrium, and means an apparatus for performing operations such as separation, concentration, recovery and purification. is doing. For example, the dehydration tower B, the light boiling separation tower (acetic acid separation tower) C, and the high boiling separation tower (acrylic acid purification tower) D shown in FIG. 1 are applicable. Similarly, the stripping tower G and the high boiling separation tower (acrylic acid refining tower) shown in FIG.
D, high boiling point removal tower H, solvent purification tower K, acrylic acid separation tower M shown in FIG. 4, alcohol recovery tower P, light boiling separation tower R,
The ester purification tower S and the distillation tower 51 shown in FIG. 5 correspond to these.

As the distillation column, there are a perforated plate column, a bubble cap column, a packed column, or a combination type of these (for example, a combination of a perforated plate column and a packed column, see FIG. 5). There is no distinction between the presence or absence of a cummer, and both can be used in the present invention. Specific trays include bubble bell trays, perforated trays, bubble trays, super flash trays, Maxflux trays, dual trays, and the like. Fillers that have been conventionally used such as columnar, cylindrical, saddle-shaped, spherical, cube-shaped, and pyramidal shapes, as well as regular or irregular packing with a special shape as high-performance packing in recent years The products are commercially available and these are preferably used in the present invention.

Examples of such commercially available products include regular packings such as Sulzer Packing (manufactured by Sulzer Brothers), Sumitomo Sruzer Packing (manufactured by Sumitomo Heavy Industries, Ltd.), and Techno Pack (Mitsui & Co.). Gauze type regular packing, Melapak (Sumitomo Heavy Industries, Ltd.), Technopack (Mitsui & Co., Ltd.), MC Pack (Mitsubishi Chemical Engineering Co., Ltd.), sheet type regular packing, Flexigrid (Cork) Examples include grid type regular packing. In addition, Gem Pack (made by Glitch), Montz Pack (made by Monts), Good Roll Packing (made by Tokyo Special Wire Mesh Co., Ltd.), Honeycomb Pack (made by NGK Insulators), Impulse Packing (made by Nagaoka)
and so on. For irregular packing, Raschig ring,
Pauling (manufactured by BASF), Cascade Mini Ring (manufactured by Mass Transfer), INTP (manufactured by Norton), Interlocks Saddle (manufactured by Norton), Terralet (manufactured by Nittetsu Kakoki), Flexi Ring (manufactured by JGC)
Etc.

The polymerization inhibitor in the present invention is a generic term for a stable radical substance, or a substance which is added to a radical to form a stable radical, or a substance which easily forms a stable radical. In some cases, it may be referred to as a polymerization inhibitor, a polymerization inhibitor, a polymerization terminator, a polymerization rate lowering agent or the like depending on the purpose, but in the present invention, it is referred to as a polymerization inhibitor.

Examples of the polymerization inhibitor include phenol compounds such as hydroquinone, methoxyhydroquinone (methoquinone), pyrogallol, catechol and resorcin; tert-butyl nitroxide, 2,2,6,6-tetramethyl-4-hydroxy. Piperidyl-1-oxyl, 2,2,6,
6-tetramethylpiperidyl-1-oxyl, 2,2,6,6-tetramethylpiperidinooxyl, 4-hydroxy-2,2,
N-oxyl compounds such as 6,6-tetramethylpiperidinooxyl, 4,4 ', 4 "-tris- (2,2,6,6-tetramethylpiperidinooxyl) phosphite; phenothiazine, bis- (Α-methylbenzyl) phenothiazine, 3,
Phenothiazine compounds such as 7-dioctylphenothiazine and bis- (α, α'-dimethylbenzyl) phenothiazine; cupric chloride, copper acetate, copper carbonate, copper acrylate, copper dimethyldithiocarbamate, copper diethyldithiocarbamate, dibutyldithiocarbamate Copper-based compounds such as copper and copper salicylate; manganese salt compounds such as manganese acetate; phenylenediamines such as p-phenylenediamine; nitroso compounds such as N-nitrosodiphenylamine; ureas such as urea; thioureas such as thiourea Can be given. These compounds may be used alone or in combination of two or more. Particularly preferred are phenothiazine and / or N-oxyl compounds from the viewpoints of polymerization inhibitory effect, corrosiveness of the distillation apparatus, and easy treatment of the waste liquid discharged from the distillation apparatus.

The most important feature of the present invention is that the inner wall surface of the distillation column is wetted with a liquid containing a polymerization inhibitor prior to the start of operation of the distillation column. As mentioned above, the polymerization inhibitor is a liquid or a solid at room temperature, but the polymerization inhibitor is not used by itself because it can prevent the polymerization of the acrylic monomer in the presence of a small amount. , Used as a solution or slurry in a given liquid medium.

Water or an organic solvent is used as the liquid medium. As the organic solvent, alcohols such as methanol, ethanol and butyl alcohol, acetone,
Ketones such as methyl ethyl ketone and methyl isobutyl ketone, carboxylic acids such as acetic acid, propionic acid, acrylic acid and methacrylic acid, aromatic hydrocarbons such as benzene, toluene and xylene, methyl acetate, butyl acetate, methyl acrylate and acrylic acid. Butyl, methyl methacrylate, ethyl methacrylate, etc. are mentioned, and these can also be used as a mixture. For example, water / toluene mixture, water / acrylic acid mixture, and crude acrylic acid containing dimer and trimer of acrylic acid (bottom liquid of acrylic acid distillation column) can be used.

As a first step for carrying out the present invention, propylene or isobutylene is subjected to vapor-phase catalytic oxidation, and an aqueous solution of acrylic acid or methacrylic acid obtained by absorbing the oxidation reaction mixture with water is concentrated in the presence of an azeotropic agent. If such a process exists, it is preferable to use the azeotropic agent as it is. The bottom liquid of the concentration tower is also suitable. Thus, when the solvent or solution used in the steps before and after the process for carrying out the present invention is selected as the liquid medium for dissolving the polymerization inhibitor, it is preferable because impurity components are not mixed. As the azeotropic agent, alcohols, ketones and aromatic hydrocarbons in the above organic solvent are preferable. The solution concentration of the polymerization inhibitor is usually 3 times or less, preferably 2 times or less the saturated solubility. Above saturation solubility,
The undissolved polymerization inhibitor will be present in the liquid, but even if these remain in the distillation column, there is no problem because they dissolve in the liquid in the column during normal distillation operation.

The method of wetting the inner wall surface of the distillation column with the liquid containing the polymerization inhibitor is not limited. Here, the inner wall surface of the distillation column refers to the vertical inner wall surface of the distillation column, as well as the tray in the case of a perforated plate distillation column, the packing in the packed column, and the tray and the packed in the combination type distillation column. The whole including both things.
As a method for wetting the inner wall surface of the distillation column, a liquid containing a polymerization inhibitor can be supplied to the reflux tank of the distillation column and supplied to the top of the distillation column from a reflux line. In order to perform sufficient wetting, the liquid containing the polymerization inhibitor supplied from the top of the column drops to the bottom of the column, so this liquid can be repeatedly supplied from the top of the column again. With the supply from the top of the tower,
It can be additionally supplied from the raw material supply stage. Distributor (liquid disperser, liquid dispersion nozzle) at the top of the packed tower
Is installed, it is preferable to supply a liquid containing a polymerization inhibitor via the distributor. This is because the liquid can be supplied into the column more uniformly.

The wetting area ratio of the inner wall surface of the distillation column is ideally 1
Although it is 00%, it is not necessarily 100% according to the recognition of the present inventors. Practically, it is assumed from the fact that a sufficient effect is achieved under the liquid flow from the reflux tank or the distributor as described above, and the small-scale experimental data that the wetted area ratio due to the flow is about 50 to 100%. In addition, the wet area ratio is 20 for which a temporary effect is recognized.
%. Therefore, in practical use, the wetted area ratio is 20% or more, preferably 40% or more, more preferably 50 to 10
0% is selected as a guide. The wet state of the inner wall of the tower, the filling material in the tower, the tray, etc. can be easily observed through a peep window (a window provided with pressure resistant glass) installed on the wall of the tower, if necessary. Also, if the conditions for wetting are determined,
Since it is not necessary to observe after that, it is not always necessary to provide the above-mentioned peep window, and the condition may be set experimentally while the operation is stopped.

In the present invention, the inner wall surface of the distillation column is wetted with the liquid containing the polymerization inhibitor, and then the operation of the distillation column is started. Most preferably, there is an embodiment in which the operation of the distillation column is started in the wet state after wetting. In a system in which a liquid containing a polymerization inhibitor flows down or is sprayed, it takes a certain amount of time for the liquid to permeate / cast into most of the inner wall surface of the distillation column. on the other hand,
After wetting the inner wall surface of the distillation column, a liquid component may evaporate and become in a dry state if a long time passes. Since the polymerization inhibitor is non-volatile even when it is in a dry state, it is maintained in a state where it is applied to the inner wall surface of the distillation column, and exhibits the effect as a polymerization inhibitor. When the vapor of the acrylic monomer is condensed on the inner wall surface of the distillation column to become a liquid, a mode in which the polymerization inhibitor is quickly dissolved in the liquid is preferable. In order to keep the dissolution rate of the polymerization inhibitor large, it is better not to dry the wet state so much. The evaporation of the liquid component depends on the type of the liquid containing the polymerization inhibitor and the atmosphere in the distillation column (operating conditions of the distillation column), but it is usually 12
Start the distillation column operation within hours, preferably within 6 hours. By doing this, the inner wall surface of the distillation column is
Alternatively, most of them are kept in a wet state, which is convenient for dissolving the polymerization inhibitor. As a mode of starting the operation of the distillation column, the raw material (crude acrylic monomer) may be supplied to the reboiler, and then the heat source may be supplied to the reboiler. The raw material may be supplied from the raw material supply stage before and after the supply of the heat source, and the supply amount may be gradually increased to shift to the steady state.

The distillation operation of the present invention can be applied to both continuous distillation and batch distillation. The operating conditions of distillation are appropriately determined in consideration of the type and content of impurities contained in the acrylic monomer, and are not particularly limited.

An example of steps for carrying out the present invention will be described below with reference to FIG. Step 1: Supply the liquid medium to the reflux tank 56. Step 2: the liquid medium of step 1 is added to the liquid supplied from the polymerization inhibitor-containing liquid tank 59 in a line 61.
Step 3 of supplying liquid to the distributor 57 through a reflux line (not shown) through No. 3; Disperse or spray a liquid containing a polymerization inhibitor from the distributor 57 to the top of the distillation column. Step 4: Start cooling with the heat exchanger 54 for cooling the overhead gas and the heat exchanger 55 for cooling the vent gas. Step 5: The liquid containing the polymerization inhibitor flows down through the packing layer and / or the perforated plate layer 52, and accumulates at the bottom of the distillation column while wetting the inner wall surface of the distillation column. After this, step 6-
1 and / or step 6-2. Step 6-1: This operation is continued for a predetermined time to sufficiently realize the wetting of the inner wall surface of the distillation column. Step 6-2: After Step 5, the liquid accumulated at the bottom of the distillation column is supplied and circulated through the line 60 and continued for a predetermined time to sufficiently wet the inner wall surface of the distillation column. Step 7: An acrylic monomer (raw material) containing a polymerization inhibitor is supplied from the line 60, and a predetermined amount of raw material is accumulated in the distillation column reboiler. Step 8: A heat source is supplied to the reboiler heating heat exchanger 58 to start the operation of the distillation column. Step 9: Start the reflux from the reflux tank 56, establish the mass balance of the supply line 60 and the lines 62, 63, 64, and shift to the steady operation.

[0032]

EXAMPLES Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist.

<Example 1> As shown in FIG.
Acrylic acid was distilled using a stainless steel (SUS316) distillation column having a length of 00 mm, a length of 20000 mm, and a Norton irregular packing (IMTP) of 8 m filled therein, and having 9 perforated plates at the bottom thereof. It was Prior to distillation
Wet operation was performed on the inner wall surface of the tower. First, a liquid 20 containing 8% by weight of methquinone as a polymerization inhibitor dissolved in acrylic acid.
kg was supplied from the top of the tower together with 500 kg of acrylic acid supplied to the reflux tank 56. Further, 40 kg of a liquid obtained by dissolving 1% by weight of phenothiazine as a polymerization inhibitor in acrylic acid was supplied from a raw material supply line 60. The supplied liquid wet the inner wall surface of the tower and dropped to the bottom of the tower. The liquid collected at the bottom of the column was supplied again from the raw material supply line 60 at 1300 kg / hr, and the circulation operation was continued for about 1 hour. About 30 minutes after that, as acrylic monomers, acrylic acid 98.5% by weight, maleic acid 0.3% by weight, acrylic acid dimer 0.
A mixture containing 3% by weight was fed at 1300 kg / hr. Further, liquids in which 8% by weight of methquinone and 1% by weight of phenothiazine were dissolved in acrylic acid were supplied from the polymerization inhibitor-containing liquid tank 59 at 34 kg / hr and 31 kg / hr, respectively. Supply a heat source, adjust the pressure in the tower, etc.
After the time, tower top pressure 2.8 kPa, tower bottom pressure 7.9 kP
a, the tower top temperature was 53 ° C, and the tower bottom temperature was 75 ° C, and stable operation was started. High-purity acrylic acid having a purity of 99.8% by weight or more was obtained from the top of the column. During operation, the pressure difference between the top and bottom of the tower (hereinafter,
The differential pressure) was stable, and continuous operation for one year was possible.

Comparative Example 1 Distillation was carried out in the same manner as in Example 1 except that the wetting operation of the inner wall surface of the column was omitted. The differential pressure increased from the start of operation, and 1
The acrylic acid purity at the top of the tower deteriorates to 2 kPa,
The operation was terminated because the liquid did not fall to the bottom of the tower. When the inside of the tower was observed after the operation was stopped, a large amount of the polymerized substance was adhering to the packing, and the adhering substance was also admitted to the tray.

Example 2 The same operation as in Example 1 was carried out except that the porous plate portion in Example 1 was changed to Norton's irregular packing (IMTP) and 6 m was filled. 1. Supply a heat source, adjust the pressure inside the tower, etc., and after about 4 hours, top pressure of the tower 2.
Stable operation was started at 8 kPa, a bottom pressure of 7.5 kPa, a top temperature of 53 ° C, and a bottom temperature of 72 ° C. Purity 9 from the top of the tower
High-purity acrylic acid of 9.8% by weight or more was obtained. During operation, the differential pressure was stable and continuous operation for one year was possible.

Comparative Example 2 Distillation was carried out in the same manner as in Example 2 except that the wetting operation on the inner wall surface of the column was omitted. The differential pressure increased from the start of operation, and 1
And the acrylic acid purity at the top of the tower deteriorates,
The operation was terminated because the liquid did not fall to the bottom of the tower. When the inside of the tower was observed after the operation was stopped, adhesion of a large amount of polymer was found in the packing.

<Example 3> The same operation as in Example 1 was carried out except that the Irregular filling (IMTP) portion manufactured by Norton was changed to 12 perforated plates in Example 1. After supplying a heat source and adjusting the pressure inside the tower, etc., after about 6 hours, the top pressure of the tower is 2.8 kP.
a, the tower bottom pressure was 8.4 kPa, the tower top temperature was 53 ° C, and the tower bottom temperature was 78 ° C, and stable operation was started. High-purity acrylic acid having a purity of 99.8% by weight or more was obtained from the top of the column. During operation, the differential pressure was stable and continuous operation for one year was possible.

Comparative Example 3 Distillation was performed in the same manner as in Example 3 except that the wetting operation of the inner wall surface of the column was omitted. The differential pressure increased from the start of the operation, and increased to 11 kPa on the 123rd day, the acrylic acid purity at the top of the tower deteriorated, and it became difficult for the liquid to drop to the bottom of the tower, so the operation was stopped. When the inside of the tower was observed after the operation was stopped, adhesion of a large amount of polymer was found on the porous plate.

<Embodiment 4> An inner diameter 11 as shown in FIG.
Distillation of crude ethyl acrylate was performed using a distillation column made of stainless steel (SUS304) having a length of 00 mm, a length of 26000 mm, and an irregular packing (IMTP) manufactured by Norton Co., Ltd. filled therein for 13 m. Prior to the distillation, the inner wall surface of the tower was wetted. First, 21 kg of a liquid containing 5% by weight of hydroquinone as a polymerization inhibitor dissolved in ethanol was added to a reflux tank 5
It was fed from the top of the tower together with 600 kg of ethanol fed to No. 6. The supplied liquid wet the inner wall surface of the tower and dropped to the bottom of the tower. The liquid collected at the bottom of the column was supplied again from the raw material supply line 60 at 6000 kg / hr, and the circulation operation was continued for about 1 hour. About 30 minutes after that, 97.4% by weight of ethyl acrylate, 1.8% by weight of water, 0.4% by weight of acrylic acid, 0.4% by weight of ethanol, and 0.1% by weight of ethyl acetate were included as acrylic monomers. 6000k for the mixture
Supplied in g / hr. Further, a liquid in which 5% by weight of hydroquinone was dissolved in ethanol was supplied from the polymerization inhibitor-containing liquid tank 59 at 60 kg / hr. After supplying a heat source and adjusting the pressure in the tower, etc., after about 6 hours, the tower top pressure is 62.7 kP
a, the bottom pressure was 69.3 kPa, the top temperature was 76 ° C, and the bottom temperature was 84 ° C, and stable operation was started. Purity 99.1 from the bottom of the tower
More than weight% of crude ethyl acrylate was obtained. driving,
The differential pressure was stable, and continuous operation for one year was possible.

Comparative Example 4 Distillation was carried out in the same manner as in Example 4 except that the wetting operation of the inner wall surface of the column was omitted. The differential pressure increased from the start of operation, and 3 days after 98 days
The operation was terminated because the temperature rose to 1 kPa, the purity of ethyl acrylate at the bottom of the column deteriorated, and the liquid did not fall to the bottom of the column. When the inside of the tower was observed after the operation was stopped, adhesion of a large amount of polymer was found in the packing.

<Embodiment 5> In Embodiment 4, the irregular packing (IMTP) portion manufactured by Norton was used as a perforated plate (dual tray).
The same operation as in Example 4 was performed except that the number of sheets was changed to 36. After supplying a heat source and adjusting the pressure inside the tower, etc., after about 7 hours, the tower top pressure is 62.7 kPa and the tower bottom pressure is 72.7 kP.
a, the tower top temperature was 76 ° C, and the tower bottom temperature was 89 ° C, and stable operation was started. Ethyl acrylate having a purity of 99.1% by weight or more was obtained from the bottom of the column. During operation, the differential pressure was stable and continuous operation for one year was possible.

Comparative Example 5 Distillation was carried out in the same manner as in Example 6 except that the wetting operation of the inner wall surface of the column was omitted. The differential pressure increased from the start of the operation and increased to 37 kPa on day 153, the purity of ethyl acrylate at the bottom of the column deteriorated, and it became difficult for the liquid to drop to the bottom of the column, so the operation was terminated. When the inside of the tower was observed after the operation was stopped, adhesion of a large amount of polymer was found on the porous plate.

<Embodiment 6> As shown in FIG.
00mm, length 18000mm, sieve tray 2 inside
Using a distillation tower made of stainless steel (SUS304) having 5 sheets, water containing ethyl acrylate as an acrylic monomer was distilled. Prior to the distillation, the inner wall surface of the tower was wetted. First, 52 kg of a liquid containing 5% by weight of hydroquinone as a polymerization inhibitor dissolved in ethanol was added to a reflux tank 5
It was fed from the top of the tower together with 1300 kg of ethanol fed to No. 6. The supplied liquid wet the inner wall surface of the tower and dropped to the bottom of the tower. The liquid collected at the bottom of the tower is fed again to the raw material supply line 60.
Then, it was supplied at 18300 kg / hr, and the circulation operation was continued for about 1 hour. About 30 minutes after that, a mixture containing 2.2% by weight of ethyl acrylate, 90.7% by weight of water, 0.1% by weight of acrylic acid and 7.0% by weight of ethanol as an acrylic monomer was supplied at 18300 kg / hr. .. Further, a liquid in which 5% by weight of hydroquinone was dissolved in ethanol was supplied from the polymerization inhibitor-containing liquid tank 59 at 18 kg / hr. Supplying a heat source, adjusting the pressure inside the tower, etc.
After the time, tower top pressure 62.7 kPa, tower bottom pressure 76.0 k
Pa, the tower top temperature was 66 ° C, and the tower bottom temperature was 92 ° C, and stable operation was started. From the top of the column, an ethyl acrylate liquid containing 67% by weight of ethanol, 21% by weight of ethyl acrylate and 12% by weight of water was obtained. During operation, the differential pressure was stable and continuous operation for one year was possible.

Comparative Example 6 Distillation was carried out in the same manner as in Example 6 except that the wetting operation of the inner wall surface of the tower was omitted. The differential pressure gradually increased from the start of operation, and 238
On the day, the temperature rose to 40 kPa, the purity of ethyl acrylate at the top of the tower deteriorated, and the liquid stopped falling to the bottom of the tower, so the operation was terminated. When the inside of the tower was observed after the operation was stopped, a large amount of polymer was found to be attached to the tray.

[0045]

According to the present invention, even if the evaporated acrylic monomer comes into contact with the inner wall surface of the distillation column and condenses, the polymerization inhibitor rapidly dissolves in the condensate, so that a polymer is produced. There is no. After the start of the operation of the distillation column, the acrylic monomer is distilled in the presence of the polymerization inhibitor, and thus no polymer is produced. Therefore, the distillation operation of the acrylic monomer can be stably performed for a long period of time.

[Brief description of drawings]

FIG. 1 is an example of a process flow diagram for producing acrylic acid from propylene as a raw material.

FIG. 2 is another example of a process flow diagram for producing acrylic acid.

FIG. 3 is another example of a process flow diagram for producing acrylic acid.

FIG. 4 is an example of a process flow diagram for producing an acrylic ester.

FIG. 5 is an example of a crude acrylic monomer distillation column and its associated equipment.

[Explanation of symbols]

A: Acrylic acid collection tower B: Dehydration tower C: Light-boiling separation tower (acetic acid separation tower) D: High-boiling separation tower (acrylic acid purification tower) E: High-boiling decomposition reactor F: Dehydration tower B and light-boiling separation Distillation tower G: Dispersion tower H: High boiling removal tower K: Solvent purification tower L: Esterification reactor M: Acrylic acid separation tower N: High boiling decomposition reactor Q : Alcohol extraction tower P: Alcohol recovery tower R: Light boiling separation tower S: Ester purification tower 1-3: Polymerization inhibitor supply line 4: Oxidation reaction gas containing acrylic acid 5: Acrylic acid aqueous solution, acrylic acid-containing solution 11 : Crude acrylic acid 15: Acrylic acid extraction line 19: High-purity acrylic acid extraction line 31: Acrylic acid supply line 32: Alcohol supply line 33: Esterification reaction mixture 35: Circulating acrylic acid 37: Extraction of high boiling impurities Line 39: Coarse acrylic Esters of extraction line 41: water supply line 42: recovered alcohol water line 46: Acrylic acid ester product extraction line 51: a distillation tower 52: filler layer, or distillation column trays, or packing,
Combined use of distillation column tray 53: Inhibitor air supply line 56: Reflux tank 57: Distributor 58: Reboiler (heat exchanger for heating) 59: Liquid tank containing polymerization inhibitor 60: Crude acrylic monomer (raw material) supply line 61 (61 1, 61 2 and 61 3): Polymerization inhibitor supply line 62: Top liquid extraction line 63: Bottom liquid extraction line 64: Vent gas discharge line

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) C07C 51/50 C07C 51/50 57/05 57/05 57/07 57/07 57/075 57/075 67 / 54 67/54 67/62 67/62 69/54 69/54 Z // C07B 61/00 300 C07B 61/00 300 (72) Inventor Yasuyuki Ogawa 1 Toho-cho, Yokkaichi-shi, Mie Mitsubishi Chemical Corporation Ceremony In-house (72) Inventor Hirochika Hosaka 1 Toho-cho, Yokkaichi-shi, Mie Mitsubishi Chemical Co., Ltd. (72) Inventor Yoshiro Suzuki 1 Toho-cho, Yokkaichi-shi, Mie Mitsubishi Chemical Co., Ltd. F-term (reference) 4D076 AA12 AA22 BB04 BB05 BB23 CB01 CC06 FA11 4H006 AA02 AB46 AC45 AC48 AD11 AD12 AD41 BA12 BA13 BA14 BA30 BC13 BS10 4H039 CA62 CA65 CD10

Claims (17)

[Claims] 1. A method of distilling acrylic acid, methacrylic acid or an ester thereof in a distillation column, wherein the inner wall surface of the distillation column is previously wetted with a liquid containing a polymerization inhibitor, and then the operation of the distillation column is started. A method for distilling acrylic acid, methacrylic acid, or an ester thereof, which comprises: 2. The method according to claim 1, wherein the distillation column is a packed column, a perforated plate column or a combined column of a packed column and a perforated plate column. 3. The method according to claim 1, wherein the liquid containing the polymerization inhibitor is an aqueous solution or an organic solvent solution. 4. The method according to claim 1, wherein the inner wall surface of the distillation column is wetted by supplying a liquid containing a polymerization inhibitor from the reflux tank of the distillation column. 5. The method according to claim 1, wherein the inner wall surface of the distillation column is wetted by supplying a liquid containing a polymerization inhibitor from a liquid disperser of the distillation column. 6. The method according to claim 1, wherein acrylic acid, methacrylic acid or an ester thereof is supplied to a distillation column together with a polymerization inhibitor. 7. The method according to claim 1, wherein acrylic acid, methacrylic acid or an ester thereof is mixed with a polymerization inhibitor and then supplied to a distillation column. 8. The distillation column inner wall surface is previously wetted with a liquid containing a polymerization inhibitor, and then the operation of the distillation column is started in the wet state.
Method described in section. 9. Acrylic acid obtained by concentrating an aqueous solution of acrylic acid or methacrylic acid obtained by vapor-phase catalytic oxidation of propylene or isobutylene and absorbing the oxidation reaction mixture with water in the presence of an azeotropic agent. Alternatively, in an operation including operation stop and operation start of the distillation column in the method for producing high-purity acrylic acid or methacrylic acid by purifying methacrylic acid in the distillation column, the inner wall surface of the distillation column is preliminarily prevented from polymerization. A method for distilling acrylic acid or methacrylic acid, which comprises wetting with a liquid containing an agent and then starting operation of a distillation column. 10. The method according to claim 9, wherein the distillation column is a packed column, a perforated plate column or a combined column of a packed column and a perforated plate column. 11. The method according to claim 9, wherein the liquid containing the polymerization inhibitor is a solution of the azeotropic agent used in concentrating the aqueous solution. 12. The method according to claim 9, wherein the liquid containing the polymerization inhibitor is a solution of acrylic acid or methacrylic acid. 13. The method according to claim 9, wherein the inner wall surface of the distillation column is wetted by supplying a liquid containing a polymerization inhibitor from the reflux tank of the distillation column. 14. The method according to claim 9, wherein the inner wall surface of the distillation column is wetted by supplying a liquid containing a polymerization inhibitor from a liquid disperser of the distillation column. 15. The method according to claim 9, wherein the acrylic acid or methacrylic acid is purified by distillation in the presence of a polymerization inhibitor. 16. Acrylic acid obtained by concentrating an aqueous solution of acrylic acid or methacrylic acid obtained by gas-phase catalytic oxidation of propylene or isobutylene and absorbing the oxidation reaction mixture with water in the presence of an azeotropic agent. Alternatively, in a method of reacting methacrylic acid with alcohol and purifying the obtained ester in a distillation column to produce an ester of acrylic acid or methacrylic acid, including the operation stop and operation start of the distillation column, the distillation column A method for distilling acrylic acid or methacrylic acid ester, wherein the inner wall surface is previously wetted with a liquid containing a polymerization inhibitor, and then the operation of the distillation column is started. 17. The method according to claim 16, wherein the inner wall surface of the distillation column is previously wetted with a liquid containing a polymerization inhibitor, and then the operation of the distillation column is started in the wet state.